The purpose of this pilot project is to develop an in vitro isolated brain stem preparation in the guinea pig in which neurophysiological and neuropharmacological studies can be performed on trigeminal reflex systems as well as on brainstem neuronal networks responsible for the generation of suckling and/or mastication. Specifically, we will establish the suitability of the in vitro preparation for the characterization of motoneuron membrane properties, synaptic and pharmacological mechanisms control trigeminal jaw opener and closer motoneuron excitability during either resting conditions, specific neuronal pathway activation or chemical stimulation. Furthermore, the ability of this preparation to produce coordinated rhythmical patterns of neuronal discharge which resemble mastication or suckling during bath application of excitatory amino acids will be determined. The project is divided into three parts. Part I will focus on recording intracellularly form trigeminal motoneurons during resting conditions for periods of time sufficient to characterize motoneuron membrane properties as well as generate synaptic potentials to peripheral reflex activation. This data will serve as normative data for further pharmacological studies. Part II will assess the role of excitatory amino acids in mediating monosynaptic and polysynaptic activation of trigeminal motoneurons during peripheral reflex activation. The ability of excitatory amino acid antagonists to antagonize reflex transmission to motoneurons will be determined. Part III will assess the ability of brainstem circuits to generate coordinated rhythmical discharges which resemble those patterns that occur during mastication of suckling during either central electrical stimulation of specific brainstem loci or pharmacological activation by excitatory amino acids. The long-term goal of this research is to understand both the mechanism underlying the central nervous system control of normal rhythmic jaw movements that occur during activities such as feeding and drinking, as well as the abnormal, involuntary rhythmic jaw movements occurring in disorders such as tardive dyskinesia and bruxism. The etiology of the generation of these abnormal jaw movements is unknown. The results of the proposed experiments will provide insights into the neurophysiological and neuropharmacological mechanisms underlying the production of normal and abnormal rhythmic jaw movements in humans.